title: Neonatal hypoxia-ischaemia disrupts descending neural inputs to dorsal raphé nuclei.
abstract: Neuronal losses have been shown to occur in the brainstem following a neonatal hypoxic-ischaemic (HI) insult. In particular serotonergic neurons, situated in the dorsal raphé nuclei, appear to be vulnerable to HI injury. Nonetheless the mechanisms contributing to losses of serotonergic neurons in the brainstem remain to be elucidated. One possible mechanism is that disruption of neural projections from damaged forebrain areas to dorsal raphé nuclei may play a role in the demise of serotonergic neurons. To test this, postnatal day 3 (P3) rat pups underwent unilateral common carotid artery ligation followed by hypoxia (6% O₂ for 30 min). On P38 a retrograde tracer, fluorescent-coupled choleratoxin b, was deposited in the dorsal raphé dorsal (DR dorsal) nucleus or the dorsal raphé ventral (DR ventral) nucleus. Compared to control animals, P3 HI animals had significant losses of retrogradely labelled neurons in the medial prefrontal cortex, preoptic area and lateral habenula after tracer deposit in the DR dorsal nucleus. On the other hand, after tracer deposit in the DR ventral nucleus, we found significant reductions in numbers of retrogradely labelled neurons in the hypothalamus, preoptic area and medial amygdala in P3 HI animals compared to controls. Since losses of descending inputs are associated with decreases in serotonergic neurons in the brainstem raphé nuclei, we propose that disruption of certain descending neural inputs from the forebrain to the DR dorsal and the DR ventral nuclei may contribute to losses of serotonergic neurons after P3 HI. It is important to delineate the phenotypes of different neuronal networks affected by neonatal HI, and the mechanisms underpinning this damage, so that interventions can be devised to target and protect axons from the harmful effects of neonatal HI.
authors.affiliation: The University of Queensland, The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital, Herston, QLD 4029, Australia.
authors.forename: H E
authors.initials: HE
authors.lastname: Reinebrant
authors.affiliation: The University of Queensland, The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital, Herston, QLD 4029, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Wixey
authors.affiliation: The University of Queensland, The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital, Herston, QLD 4029, Australia. Electronic address: k.buller@uq.edu.au.
authors.forename: K M
authors.initials: KM
authors.lastname: Buller
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D016923:Cell Death; D065847:Dorsal Raphe Nucleus / Q000473:pathology*; D004525:Efferent Pathways / Q000473:pathology*; D007031:Hypothalamus / Q000473:pathology; D020925:Hypoxia-Ischemia, Brain / Q000473:pathology*; D056325:Neuronal Tract-Tracers / Q000737:chemistry; D017397:Prefrontal Cortex / Q000473:pathology; D011301:Preoptic Area / Q000473:pathology; D016548:Prosencephalon / Q000473:pathology*; D051381:Rats; D059326:Serotonergic Neurons / Q000473:pathology*
chemical_list: D056325:Neuronal Tract-Tracers
keywords: choleratoxin subunit b; dorsal raphé nuclei; hypoxia–ischaemia; neonate; retrograde tracing; serotonin